Introduction to Community Interactions - Online Tutor, Practice Problems & Exam Prep

Community ecology examines interspecific interactions among populations in a shared environment, influencing fitness and evolution. Key interactions include commensalism, competition, predation, and mutualism. The ecological niche defines an organism's role, with fundamental and realized niches reflecting survival conditions. Competitive exclusion and niche differentiation help species coexist. Predation shapes populations, with adaptations like constitutive and inducible defenses, including aposematic and cryptic coloration. Symbiosis, such as mutualism and parasitism, highlights complex relationships, impacting community dynamics and species survival.

Introduction to Community Interactions

This video, we're going to begin our introduction to community interactions. A community interaction is really just a relationship between two or more organisms in a community, and they can be classified either as intraspecific or interspecific interactions. Now, an intraspecific interaction is going to occur between organisms of the same exact species. Whereas, on the other hand, interspecific interactions occur between organisms of different species. Moving forward in our course, these interspecific interactions are going to be the primary focus of our lesson.

So, let's take a quick look at our image below where on the left-hand side, we're showing you an example of an intraspecific interaction occurring between organisms of the same species. Here, we're looking at two bighorn sheep colliding with each other perhaps to establish dominance for mating purposes. Now, on the right-hand side, we're showing you an example of an interspecific interaction between organisms of different species. Here, a bighorn sheep and a spotted deer competing for the same food resource. Now intra and inter sound really similar to each other.

One way that helps me differentiate the two is that the TRA in Intraspecific reminds me of the TRA in the word "trapped". So I know that these Intraspecific interactions are somewhat trapped within the same species and only occur between organisms of the same species. Whereas, of course, interspecific interactions are not trapped, so they occur between organisms of different species. So that concludes this video, and we'll be able to learn more about community interactions moving forward. So see you all in our next video.

Which of the following is unique to intraspecific interaction?

• A. Food availability.
• B. Space/shelter.
• C. Sunlight.
• D. Access to a mate for breeding.

Overview: Types of Community Interactions

This video, we're going to briefly overview the types of community interactions. But moving forward in our course, we'll get to talk a lot more details about all of these community interactions in their own separate videos. Now community interactions are classified based on their effect on the organism's fitness. And so community interactions can either have a positive, negative, or a neutral effect on the organism's fitness. A positive effect is symbolized with a plus symbol.

A negative effect is symbolized with a minus symbol, and a neutral effect is symbolized with the number 0. And so we can actually pair up these three different symbols here to create four primary types of community interactions, which we're showing you down below in this table. And so the first type is competition, which is a minus minus interaction where both organisms are negatively affected, such as, for example, lions and hyenas fighting and competing for the same resource. Now the next type is exploitation, which in some textbooks is also referred to as consumption. And this is a plus minus interaction, meaning that one organism benefits while the other organism is harmed.

And there are three different types which are predation, herbivory, and parasitism. And so notice in this image, this chameleon here is consuming and exploiting this insect. Now the last two types of community interactions are often grouped together as positive interactions since they are plus plus and plus 0. And so plus plus interactions are mutualism where both organisms benefit from the interaction, such as the interaction between these clownfish and these sea anemones here, where the sea anemones provide the clownfish with shelter and protection, and the clownfish will consume parasites and clear debris for these sea anemones. So both organisms are benefiting.

Now commensalism is a plus zero interaction where one organism benefits and the other organism is neutrally affected, meaning that it neither benefits nor is harmed. And so an example of that are these flowers growing on this tree, where the flowers are benefiting from the interaction because they're able to get better access to sunlight. But the tree itself is neither benefiting nor being harmed, and so it is neutrally affected. Now the last note that I'll leave you all off with is that the type of interaction between 2 organisms is not necessarily stuck as the same type of interaction forever. Instead, the type of interaction is actually subject to change over time.

And so this is something to keep in the back of your head as we move forward, discussing this more and more. So that concludes this overview and I'll see you all in our next video.

Introduction to Community Interactions Example 1

So here we have an example problem that says, suppose you remove species a from a community, which you notice reduces the fitness of species b. After introducing species a back into the community, you then remove species b and find that it has no significant impact on the fitness of species a. What is the relationship between species a and species b? And we've got these 4 potential answer options down below. Now to solve this problem, I've gone ahead and drawn a little sketch, which you can see right here, to help us better visualize what's happening in this problem.

Notice on the far left, we've got the community with both species a and species b present. But then we remove species a and find that it has a negative impact on the fitness of species b, indicated by the minus sign here. Then we reintroduce species a back into the community and remove species b, and find that that has no impact on the fitness of species a, indicated by the 0 here. And so what this seems to indicate is that species b has no effect on the fitness of species a, so we can put a 0 there. And because species b's fitness goes down in the absence of species a, that suggests that species a helps to improve the fitness of species b.

So we can put a plus sign for that. And so this is a plus-zero interaction, which is commensalism. Notice that we can eliminate answer option a, which says mutualism. That's a plus-plus interaction where both organisms benefit. That's not the case here.

We can eliminate option b, which says competition. That's a minus-minus interaction where both organisms are negatively impacted. And again, that's not the case here. So now we're between either option c or option d, which both say commensalism. But notice that it's species b that benefits, and species a that is unaffected.

So that matches with answer option c, which says commensalism where species b benefits while species a is unaffected. So we can go ahead and indicate that c here is the correct answer to this example problem, and d is not correct because it says species a benefits while species b is unaffected, but it's the other way around. Species b is benefiting, species a is unaffected. So c here is the correct answer. That concludes this problem, and I'll see you all in our next video.

Which of the following statements is true?

• A. An interaction where both organisms benefit is called competition.
• B. An interaction where neither organism benefits is called mutualism.
• C. In mutualism, only one organism benefits.
• D. The type of interaction between two organisms is potentially subject to change over time.

Here’s what students ask on this topic:

What are the different types of interspecific interactions in community ecology?

Interspecific interactions in community ecology include commensalism, competition, predation, and mutualism. Commensalism occurs when one organism benefits while the other is unaffected. Competition is negative for both organisms involved as they vie for the same resources. Predation involves one organism (the predator) consuming another (the prey), which can include herbivory (animals eating plants) and parasitism (one organism benefits at the expense of another). Mutualism is a positive interaction for both organisms, where both species benefit from the relationship. These interactions significantly impact the survival, reproduction, and evolution of the species involved.

What is the difference between a fundamental niche and a realized niche?

A fundamental niche encompasses all the environmental conditions suitable for an organism's survival and reproduction, ignoring interspecific interactions. It represents the full potential range of conditions an organism can theoretically occupy. In contrast, a realized niche is the actual portion of the fundamental niche that an organism occupies due to limiting factors such as competition, predation, and other interspecific interactions. The realized niche is typically smaller than the fundamental niche because these interactions restrict the organism's ability to exploit all available resources.

How does the competitive exclusion principle affect species coexistence?

The competitive exclusion principle states that two species competing for the same resources cannot coexist indefinitely. If two species occupy the same niche without any environmental disturbances, one species will outcompete the other, leading to the extinction of the less competitive species. To coexist, species often undergo niche differentiation, where they modify their resource use to reduce direct competition. This can involve resource partitioning, where species use different resources or the same resources in different ways, allowing them to coexist more harmoniously.

What are constitutive and inducible defenses in prey species?

Constitutive defenses are always present in an organism, regardless of the presence of predators. Examples include physical traits like thorns on plants or the stick-like appearance of stick bugs. Inducible defenses, on the other hand, are activated in response to predator presence. These can be physical, behavioral, or chemical traits. For instance, a skunk's chemical spray is an inducible defense that is only used when threatened. Both types of defenses play crucial roles in the evolutionary arms race between predators and prey.

What is mimicry, and what are its types?

Mimicry is an evolved defense mechanism where one organism resembles another to gain an advantage. There are two main types: Batesian mimicry and Müllerian mimicry. In Batesian mimicry, a harmless species imitates the warning signals of a harmful species to deter predators. An example is the non-poisonous king snake mimicking the poisonous coral snake. In Müllerian mimicry, two harmful species evolve to look similar, reinforcing the avoidance behavior in predators. An example is the similarity between the bad-tasting monarch and viceroy butterflies. Both types of mimicry enhance the survival of the mimicking species.